SWCU194 March 2023 CC1314R10 , CC1354P10 , CC1354R10 , CC2674P10 , CC2674R10
The following four basic frame formats can be selected through SPI:CTL0.FRF field:
For all four formats, the serial clock (SPIn_CLK) is held inactive while the SPI is idle and SPIn_CLK transitions at the programmed frequency only during active transmission or reception of data. The IDLE state of SPIn_CLK provides a receive time-out indication that occurs when the RX FIFO still contains data after a time-out period.
For Motorola SPI (4-wire) and MICROWIRE frame formats, the serial frame (SPIn_CS) pin is active low and is asserted (pulled down) during the entire transmission of the frame.
For TI synchronous serial frame format, the SPIn_CS pin is pulsed for one serial clock period which starts at its rising edge before the transmission of each frame. For this frame format, both the SPI and the off-chip slave device drive their output data on the rising edge of SPIn_CLK and latch data from the other device on the falling edge.
Unlike the full-duplex transmission of the other three frame formats, the MICROWIRE format uses a special master-slave messaging technique that operates at half-duplex. When a frame begins, an 8-bit control message is transmitted to the off-chip slave. No incoming data is received by the SPI during this transmission. After the message is sent, the off-chip slave decodes it and responds with the requested data after waiting one serial clock after the last bit of the 8-bit control message is sent. The returned data can be 4 to 32 bits long (master mode) or 7 to 32 bits (slave mode), making the total frame length anywhere from 13 to 41 bits.